Semiconductor devices are typically fabricated on a substrate that provides mechanical support for the device and often contributes to the electrical performance of the device as well. Silicon, germanium, gallium arsenide, sapphire and silicon carbide are some of the materials commonly used as substrates for semiconductor devices. Many other materials are also used as substrates. Semiconductor device manufacturing typically involves fabrication of many semiconductor devices on a single substrate.
Substrates are typically formed in the shape of circular wafers having a diameter presently ranging, for example, from less than 1 inch (2.54 cm) to over 12 inches (30.5 cm) depending on the type of material involved. Other shapes such as, for example, square, rectangular or triangular wafers are possible, however. Semiconductor devices are formed on the wafers by the precise formation of thin layers of semiconductor, insulator and metal materials which are deposited and patterned to form useful semiconductor devices such as diodes, transistors, solar cells and other devices.
Individual semiconductor devices are typically extremely small compared to the size of the wafer on which they are formed. For example, a typical light emitting diode (LED) chip such as the C430-XB290 LED chip manufactured by Cree, Inc., in Durham, N.C. measures only about 290 microns by 290 microns square (1 micron=0.0001 cm). Accordingly, a very large number of LED chips (also referred to as “die”) may be formed on a single 2 inch (5.08 cm) diameter silicon carbide (SiC) wafer. After the die are formed on the wafer, it is necessary to separate at least some of the individual die so that they can be mounted and encapsulated to form individual devices. The process of separating the individual die is sometimes referred to as “dicing” or “singulating” the wafer.
Dicing a wafer into individual semiconductor devices may be accomplished by a number of methods. One method of dicing a wafer involves mounting the wafer on an adhesive surface and sawing the wafer with a circular saw to form a number of individually diced, square or rectangular shaped devices. Other methods of dicing include “scribe-and-break” techniques. In these methods, one or more trenches or scribe lines are formed in a surface of the wafer using a saw or ablation by laser. The wafer is then subjected to a load sufficient to break the wafer into individual dice. The scribe lines present lines of weakness in the wafer so that the wafer breaks along the scribe lines.
Singulation considerations may be particularly significant in the manufacture of light emitting diodes (LEDs). LEDs are widely used in consumer and commercial applications. As is well known to those having skill in the art, a light emitting diode generally includes a diode region on a microelectronic substrate. The microelectronic substrate may comprise, for example, gallium arsenide, gallium phosphide, alloys thereof, silicon carbide and/or sapphire. Continued developments in LEDs have resulted in highly efficient and mechanically robust light sources that can cover the visible spectrum and beyond. These attributes, coupled with the potentially long service life of solid state devices, may enable a variety of new display applications, and may place LEDs in a position to compete with the well entrenched incandescent lamp. GaN-based light emitting diodes (LEDs) typically comprise an insulating, semiconducting or conducting substrate such as sapphire or SiC on which a plurality of GaN-based epitaxial layers are deposited. The epitaxial layers comprise an active region having a p-n junction that emits light when energized.